In the rebuilding of gas turbine engines, usually the tip surfaces of the high pressure turbine blades are worn or eroded resulting in an undesirable clearance or gap between the tip surfaces and the surrounding stator. While it is sometimes possible to rebuild the blade tips by applying a weld bead, the welding operation produces weld flash which projects laterally from the tips of the blades, and the flash must be removed by grinding. Since the blades have a tapered contoured peripheral surface, the weld flash is usually removed manually by grinding with handheld grinders or grinding belts. This manual grinding operation requires considerable labor and high dexterity. It is also difficult to grind the weld flash so that the coutoured weld surface forms a smooth and flush continuation of the tapered blade surface around the entire periphera of the blade.
It has been determined that it would be very desirable to perform the grinding operation on each blade with an automatic grinding machine which removes the weld flash from the tip of each blade and forms a contoured weld surface on the tip which is a smooth continuation or extension of the contoured tapered blade surface. It is also desirable for the automatic grinding machine to assure that the grinding wheel is prevented from moving below the surface of the blade to avoid producing any recess or defect which requires scrapping of the blade or reduces it performance. Since the turbine blades vary in size and shape, it is also desirable to provide for conveniently programming the automatic grinding machine according to the size and contour of a finished blade and to provide for conveniently adjusting certain moveable components of the machine to assure precision contour grinding of each blade.
One form of automated edge finishing machine is disclosed in U.S. Pat. No. 5,261,768. In this apparatus or machine, the workpiece is mounted on an X-Y table which moves the workpiece around a rotating deburring, grinding or finishing tool. The path of the workpiece is preprogrammed into the control system for the machine, but no mechanism is provided for accommodating a workpiece having tapering or converging outer contoured surfaces such as the outer surfaces of a high pressure gas turbine blade. Other forms of automatic surface finishing machines are disclosed in U.S. Pat. Nos. 4,894,597 and 4,993,896 which are referred to in column one of U.S. Pat. No. 5,261,768.